How to name dark fungal taxa outside the Code: The International Standard to Catalogue Dark Fungal Taxa (ISCDFT)

There is an exponential increase in the number of fungal OTUs being documented by environmental DNA (eDNA) metabarcoding. Many of these, the so-called dark fungal taxa (DFT), are known only from eDNA data, with no associated physical specimen or derived culture. Of the millions of fungal species predicted to exist, only ~205,000 are currently described, making it likely that many of these unknown or undescribed fungi are represented only by eDNA data. For more than a decade mycologists have struggled with whether the International Code of Nomenclature for algae, fungi, and plants (the Code ) should allow for formal description of fungal taxa from eDNA data alone, i.e. with a DNA sequence serving as a type. It is, however, unlikely that an amendment to the Code with this provision will pass in the near future. It is therefore imperative to establish an informal yet structured naming system to allow unified communication about DFT. The system proposed herein applies most of the principles of the Code to generate designations that, while nomenclatorially invalid, can nonetheless be integrated into fungal classifications and diversity assessments. We used the 2025 Westerdijk Spring Symposium "DNA Sequences as Type" to bring mycologists together to work out community consensus-driven conventions and standards for what we call the International Standard to Catalogue Dark Fungal Taxa (ISCDFT). The established guidelines principally refer to naming conventions, quality and standards for the underlying data, and standards regarding the underlying analysis leading to the detection of new DFT. The ISCDFT does not compete with the Code but enables the community to catalogue DFT and integrate these into fungal classifications while adhering to broadly established principles. For ease of immediate implementation, we provide examples to illustrate these newly established guidelines, a checklist for publishing new DFTs under the ISCDFT, and convert some previously published fungal names based on eDNA sequences to ISCDFT-compliant names.